Farm-Scale Estimation of Total Nitrogen Content in Surface Paddy Soils by Extraction with Commercially Available Hydrogen Peroxide
Naoki Moritsuka | Hiroki Saito | Ryosuke Tajima | Yukitsugu Takahashi | Hideaki Hirai
We recently proposed a simple method for estimating total nitrogen content in paddy soil. In this method, soil is extracted with a commercial 3% hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) solution at 25 °C for 40 h, and electrical conductivity (EC (H<sub>2</sub>O<sub>2</sub>)) of the extract is measured. This study aimed to further evaluate the method’s applicability to soil samples collected at the farm scale by using the original and six additional H<sub>2</sub>O<sub>2</sub> solutions that are locally and commercially available. The results obtained with the original solution indicated that the determination coefficients between EC (H<sub>2</sub>O<sub>2</sub>) and total N were statistically significant at all farms examined: Moka, 0.78 (<i>n</i> = 13); Kyoto, 0.50 (<i>n</i> = 16); Kizu, 0.43 (<i>n</i> = 89); and Kawatabi, 0.25 (<i>n</i> = 18). The EC of the tested H<sub>2</sub>O<sub>2</sub> solutions varied from less than 0.05 to 1.4 mS cm<sup>−1</sup> because of the addition of different stabilizers. EC (H<sub>2</sub>O<sub>2</sub>) values obtained with the less stabilized H<sub>2</sub>O<sub>2</sub> solutions (one from Japan, one from USA, and the analytical grade 6% solution) agreed well with those obtained with the original solution. Thus, the proposed method can be useful for estimating the farm-scale variation in soil total N, provided a H<sub>2</sub>O<sub>2</sub> solution with a low EC (<0.2 mS cm<sup>−1</sup>) is used for the extraction.
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